ObjectiveTo describe the clinical characteristics, electrodiagnostic, and imaging findings of Hirayama disease (HD), late onset monomelic amyotrophy (LMA), and brachial amyotrophic diplegia (BAD).

MethodA retrospective analysis of the medical records, electrodiagnostic, and imaging findings of 12 patients (4 HD, 2 LMA, 6 BAD) was done. For patients whose last clinic follow-up exceeded 6 months a telephone survey was done to see if there were any symptom changes.

ResultsThe clinical, electrodiagnostic, and imaging findings of the HD and BAD patients were similar to previous studies. Except for a later onset, age disease duration was too short to distinguish LMA from HD or other motor neuron diseases. One patient in the BAD group progressed to amyotrophic lateral sclerosis (ALS) and another died due to undetermined respiratory failure. These two patients showed abnormalities in their lower extremities, thoracic paraspinal, and craniocervical muscles on needle electromyography. Except for another patient, none of the other three patients showed abnormalities in their lower extremities, thoracic paraspinals, or craniocervical muscles on needle electromyography.

ConclusionHD and BAD can be considered as separate disease entities. However, a longer follow-up period than previously recommended is necessary to differentiate BAD from ALS. Follow-up period was too short to determine whether LMA can also be considered as a separate disease entity.

Hirayama disease is characterized by focal amyotrophy of the upper limb associated with unilateral or asymmetric bilateral muscle weakness. It occurs in young men in their late teens or early twenties. Repeated or sustained neck flexion is thought to be a cause of the disease. It is important to prevent the progression of the disease through early recognition and management. We reported a patient with Hirayama disease in order to review the typical clinical, electrodiagnostic and radiological findings of Hirayama disease. (J Korean Acad Rehab Med 2004; 28: 387-391)